The present invention relates to a metal vapor discharge lamp.
As a conventional metal vapor discharge lamp, for example, a metal halide lamp, a lamp having a configuration in which a discharge tube is enveloped by a glass cylindrical sleeve (hereinafter, xe2x80x9csleevexe2x80x9d will be referred to) in order to prevent an outer tube from being damaged due to the rupture of the discharge tube at the end of the lifetime, with both ends of the sleeve being closed by a metal plate is proposed (JP2 (1990)-230655 A).
This metal plate is provided with a tongue piece that is brought into contact with the outer tube and the sleeve respectively. By bringing the tongue piece into contact with the inner surface of the outer tube, the sleeve is allowed to be held in the predetermined portion in the outer tube.
Furthermore, in recent years, such a conventional metal halide lamp uses a translucent ceramic discharge tube that is excellent in thermal resistance or halogen resistance. A conventional metal halide lamp using this translucent ceramic discharge tube includes a light-emitting portion and thin tube portions. Inside the light-emitting portion, an electrode is disposed in which a metal halide (a light-emitting metal) and the like is filled. The thin tube portions are provided at both ends of the light emitting portion and include a feeding body made of a conductive cermet, niobium, or the like sealed with a sealing material.
However, in such a conventional metal halide lamp, when the lamp is turned on, heat radiated from the discharge tube remains in a space formed by the sleeve and the metal plate. In particular, in a metal halide lamp using a translucent ceramic discharge tube, due to the difference in the coefficient of thermal expansion between the thin tube portion and the sealing material and between the feeding body and the sealing material, cracks tend to occur in the sealed portions. Furthermore, a reaction between the metal halide and the sealing material is promoted, thus deteriorating the sealing material, which may cause the leakage in the discharge tube. Consequently, the lifetime of lamp is shortened.
Moreover, the sealing portion herein denotes a sealing material and a portion of the thin tube portion sealed with the sealing material.
Furthermore, since both ends of the sleeve are closed with the metal plate, light traveling toward the direction of the closed portion side of the outer tube is shielded by the metal plate, thus deteriorating the light flux.
Furthermore, since the outer tube is in contact with the tongue piece of the metal plate positioned on the closed portion side of the outer tube, after the lamp is turned on or off, when the discharge tube is thermally-expanded or thermally-shrunk, the metal plate moves following the thermal expansion or thermal shrinkage, and at this time, the tongue piece rubs against the inner surface of the outer tube, thus to make an abnormal noise.
With the foregoing in mind, it is an object of the present invention to provide a highly efficient and long lifetime metal vapor discharge lamp capable of suppressing the occurrence of abnormal noises after the lamp is turned on or off with a sleeve supported firmly.
In order to achieve the above-mentioned object, the metal vapor discharge lamp according to the present invention includes an outer tube having a closed portion at a first end and a base at a second end; a discharge tube inside of which an electrode is provided, located in the outer tube; and a sleeve enveloping the discharge tube and located in the outer tube, wherein the sleeve includes an open portion on the closed portion side of the outer tube; the closed portion side of the outer tube is provided with a support for supporting an end of the closed portion side of the sleeve; the support includes a column portion having a narrow plate shape or a narrow stick shape separated from the open portion of the closed portion side of the sleeve, and a sleeve holding portion provided at an end of the column portion and is in contact with the sleeve; and the support is connected to a feeding body connected to the electrode and led from the discharge tube toward the side of the closed portion, and connected to an electric power supply wire extending toward the side of the base.
According to this configuration, since the amount of light flux emitted from the sleeve can be increased with the sleeve supported firmly, and the sleeve can be opened to the greatest extent practicable, it is possible to prevent heat from building up in a space enveloped by the sleeve. Furthermore, since the lamp of the present invention does not use the tongue piece unlike the conventional lamp, it is possible to suppress the occurrence of abnormal noises after the lamp is turned on or off.